I think providing nutrients via the substrate in a non-CO2 enriched tank will tip the competion scale in favor of plants that utilize roots as a primary nutrient source. The problem arises when we keep a variety, some of which rely on water column soley for nutrients. Then those plants can suffer as a result although there is leeching of nutrients from the substrate which sustains those plants. It seems to me that several methods could exist based on the plant varieties we are trying to grow. Presently, to grow a variety, the best solution is to dose both the substrate and water column. In that system, a large biomass of plants we want will outcompete the algae, which is what has been stated by the experts time and time again. It seems the more I learn the more I say to myself "huh that's what that guy already said"